The fifteen serovars (immunotypes) of Chlamydia trachomatis represent a model for determining the biologic significance of the antigenic diversity often found in membranes or other surface proteins of bacterial pathogens. We will present plans to test the hypothesis that the domains of C. trachomatis major outer membrane protein which vary antigenically among these serovars have a role in the pathogenesis of chlamydial infection. We have cloned genes expressing the major outer membrane proteins (MOMP) of C. trachomatis serovars L1 and K in E. coli. Based upon knowledge of the DNA sequence derived amino acid sequence of MOMP we will be able to create a model of MOMP structure in the C. trachomatis outer membrane. The antigenically variable domains of MOMP will be identified in relation to surface exposure. Structure-function relationships of MOMP will be determined in systems to assess neutralization of infectivity, attachment, and toxicity to eucaryotic cells.